CN211442545U

CN211442545U - Mobile robot chassis

Info

Publication number: CN211442545U
Application number: CN201922257802.1U
Authority: CN
Inventors: 蔡佳豪; 李金波; 明振
Original assignee: Changsha Wanwei Robot Co ltd
Current assignee: Changsha Wanwei Robot Co ltd
Priority date: 2019-12-12
Filing date: 2019-12-12
Publication date: 2020-09-08
Anticipated expiration: 2029-12-12

Abstract

The utility model discloses a mobile robot chassis, which comprises a framework, an upper cover, a side plate and a steering wheel assembly; the framework is a box body with a sunken middle part, the periphery of the framework is provided with a plurality of mutually independent wheel grooves, the upper edge of the framework is provided with support angles, and a slot is arranged between two adjacent support angles; the upper cover is arranged on the upper part of the closed framework on the supporting angle, the side plate is inserted into the slot to close the side surface of the framework, and each steering wheel assembly is respectively arranged in the corresponding wheel groove. A plurality of mutually independent steering wheel assemblies are respectively arranged in corresponding wheel grooves at the lower part of the framework, so that the steering flexibility is improved, and each steering wheel assembly is mutually independent, has independent drive and adopts an independent suspension form, so that the obstacle crossing capability of the steering wheel assembly is improved.

Description

Mobile robot chassis

Technical Field

The utility model belongs to the technical field of the robot, especially, relate to a mobile robot chassis.

Background

The chassis of the existing wheeled robot generally adopts a structure that the front universal wheels and the rear universal wheels are arranged in a diamond shape, and the chassis is driven by the left and the right driving wheels through differential speed, so that the chassis has the advantages of simple control mode and zero movement, but can only be applied to a completely flat environment. Some robot chassis adopt two drive wheels in the front, the chassis structure of one or two universal wheels in the back, and this type of chassis arranges into squarely generally, and although possess certain ability of hindering more, in stability relatively poor, can not realize pivot and turn to, zero activity is not enough. Some robot chassis adopt four-wheel drive or crawler-type drive wheel's mode, and it is superior in the aspect of heavy load and obstacle crossing, nevertheless have the wheel to slide in the course of turning, cause the wheel speed feedback unreal, the error is big, is difficult to do accurate control.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to prior art's weak point, provide a turn to nimble mobile robot chassis that just hinders the ability reinforce more.

The utility model provides a chassis of a mobile robot, which comprises a framework, an upper cover, a side plate and a steering wheel assembly; the framework is a box body with a sunken middle part, the periphery of the framework is provided with a plurality of mutually independent wheel grooves, the upper edge of the framework is provided with support angles, and a slot is arranged between two adjacent support angles; the upper cover is arranged on the upper part of the closed framework on the supporting angle, the side plate is inserted into the slot to close the side surface of the framework, and each steering wheel assembly is respectively arranged in the corresponding wheel groove.

In a specific embodiment, the framework is a rectangular box body, the middle of the rectangular box body is a cross-shaped sinking cavity, four corners of the rectangular box body are steering engine mounting positions, through holes are formed in the top surfaces of the steering engine mounting positions, and mounting holes are formed in the periphery of the through holes.

Preferably, the supporting angle comprises an outer plate and a supporting plate, the outer plate is an L-shaped plate attached to the corner of the framework, the supporting plate is a right-angle triangular plate, the top of the right angle is an arc attached to the outer plate, a clamping groove parallel to the right-angle side and penetrating through the bevel edge is formed in the supporting plate, and the supporting plate is connected to the top of the outer plate.

In order to improve the installation accuracy, the top of outer plywood is equipped with the flange, the outer fringe of backup pad is equipped with the draw-in groove, welds after backup pad and outer plywood block.

Preferably, the inner layer plate is an integral piece and comprises triangular sections at two ends and a connecting section in the middle, each inner layer plate is respectively erected on the framework and arranged in parallel with the outer layer plate, the triangular sections at two ends of one inner layer plate are provided with hinges, and the other ends of the hinges are connected with the upper cover; each side plate is arranged in the inner-layer plate.

Furthermore, a radar support is arranged in the middle of the upper cover.

In one embodiment, the steering wheel assembly includes a drive wheel module and a steering module; the driving wheel module comprises a wheel body, a driving motor and a damping bracket, and the driving motor is connected with the driving wheel through the damping bracket; the steering module comprises a steering motor, a speed reducing mechanism and a rotating shaft, wherein an output shaft of the steering motor is connected with an input end of the speed reducing mechanism, an output end of the speed reducing mechanism is connected with the rotating shaft, and the other end of the rotating shaft is connected with the damping support; the driving motor drives the wheel body to rotate; the output power of the steering motor is transmitted to the rotating shaft to drive the damping support to steer after being decelerated by the decelerating mechanism.

Further, the shock absorption support comprises a lower support, an upper support, a shock absorber and a hinge seat; the lower bracket is a U-shaped bracket, and the middle parts of the two side plates are provided with through holes; the upper bracket is an n-shaped bracket which is obliquely arranged downwards, the top end of the upper bracket is provided with a circle of connecting holes, and the lower end of the upper bracket is hinged outside the lower bracket; the pair of shock absorbers are symmetrically arranged on the central plane of the wheel body in the thickness direction and are respectively arranged on the two sides of the upper bracket and the lower bracket; pin shafts are welded on two sides of the lower support, pin shafts are welded on two sides of the upper support, radial holes are formed outside the pin shafts, and two ends of the shock absorber are respectively sleeved outside the pin shafts and are positioned through split pins penetrating through the radial holes; a through hole is formed in the center of the hinge seat, a circle of connecting holes are formed in the periphery of the hinge seat, and a wear-resistant sleeve is embedded in the through hole; the hinged seat is connected with the upper bracket through a bolt penetrating through the connecting hole, and the upper bracket is sleeved outside the lower bracket and is connected with the lower bracket through a rotating shaft bolt penetrating through the wear-resistant sleeve; the rotating shaft bolt comprises a cylindrical head, a polished rod section and a threaded section, the outer diameter of the cylindrical head is gradually decreased, the cylindrical head is a hexagon socket head, the rotating shaft bolt is sleeved in the wear-resistant sleeve through the polished rod section, and the threaded section is in threaded connection with the lower support.

Preferably, the driving motor is a hub motor, threads are arranged at two ends of a central shaft of the hub motor, and planes are arranged at the outer ends of the thread sections; the driving motor is embedded in the wheel body, and the central shaft penetrates through the upper through hole of the lower bracket and is locked by matching with the nut; the speed reducing mechanism comprises a main speed reducer and an auxiliary speed reducer, the input end of the main speed reducer is connected with the steering motor, the output shaft of the main speed reducer is connected with the input gear of the auxiliary speed reducer, and the output end of the auxiliary speed reducer is connected with the rotating shaft; both ends of an output shaft of the main speed reducer extend out of the main speed reducer, and a strong magnetic steel sleeve is arranged outside the top end of the output shaft; an angle sensor is arranged at the position corresponding to the ferromagnetic steel sleeve under the steering motor; the shell of the auxiliary speed reducer comprises an upper shell and a lower shell, a circle of groove is formed in the outer edge of the upper shell, a matched protrusion is formed in the outer edge of the lower shell, and the upper shell and the lower shell are matched with the protrusion through the groove to improve installation accuracy.

In order to further improve the shock attenuation effect, the pivot is the step shaft, and the top of pivot is equipped with the jack catch of evagination, establishes the draw-in groove in the output gear of vice reduction gear, and the pivot links to each other with its top and vice reduction gear, and the jack catch extends in the draw-in groove and packs the cushion rubber, with its bottom with shock absorber support links to each other through the bolt that passes the connecting hole.

The utility model discloses set up a plurality of mutually independent steering wheel assemblies respectively in the race that the skeleton lower part corresponds, do benefit to the flexibility that improves and turn to each steering wheel assembly mutually independent all has independent drive, adopts the form of independent suspension, can improve its ability of hindering more.

Drawings

Fig. 1 is an axial view of a preferred embodiment of the present invention.

Fig. 2 is an exploded view of the preferred embodiment.

Fig. 3 is an axial view of the skeleton in the preferred embodiment.

Fig. 4 is an enlarged schematic view of the steering wheel assembly in the preferred embodiment.

Fig. 5 is an enlarged schematic axial view of the driving wheel module in the preferred embodiment.

Fig. 6 is a schematic cross-sectional view of a-a in fig. 5.

Fig. 7 is an enlarged schematic view at B in fig. 6.

Fig. 8 is a schematic sectional view of the steering module in the present preferred embodiment.

Fig. 9 is a schematic cross-sectional view of C-C in fig. 8.

Sequence numbers of the drawings:

1-framework, 11-cross cavity, 12-wheel groove, 13-through hole, 14-mounting hole, 15-supporting angle, 151-outer plate, 152-supporting plate and 16-inner plate;

2-upper cover, 21-radar support;

3, side plates;

4-a steering wheel assembly is arranged on the steering wheel assembly,

41-driving wheel module, 411-wheel body, 412-driving motor,

413-damping support, 4131-lower support, 4132-upper support, 4133-damper, 4134-pin shaft, 4135-hinged seat, 4136-wear-resisting sleeve, 4137-rotating shaft bolt, 4138-split pin;

42-steering module, 421-steering motor,

422-speed reducing mechanism, 4221-main speed reducer, 4222-auxiliary speed reducer,

423-rotating shaft, 4231-claw,

424-strong magnetic steel sleeve, 425-angle sensor, 426-shock absorption rubber cushion;

5-a hinge.

Detailed Description

As shown in fig. 1 and fig. 2, the mobile robot chassis disclosed in this embodiment includes a frame 1, an upper cover 2, a side plate 3, and a steering wheel assembly 4.

As shown in fig. 3, the frame 1 is a sinking rectangular box, the middle part of the frame is a sinking cross cavity 11, four corners of the frame are wheel grooves 12 for mounting the steering wheel assembly 4, a through hole 13 for passing through a steering module in the steering wheel assembly is arranged on the body of the frame 1, mounting holes 14 for locking the steering wheel assembly are arranged around the through hole, and supporting angles 15 are arranged on the upper edges of the four corners of the through hole for mounting an upper module. The supporting angle 15 comprises an outer plate 151 and a supporting plate 152, the outer plate 151 is an L-shaped plate attached to the corner of the framework, the supporting plate is a right-angle triangular plate, the vertex of the right angle is an arc attached to the outer plate, a clamping groove parallel to the right-angle edge and penetrating through the bevel edge is formed in the supporting plate, and the supporting plate is connected to the top of the outer plate. The top of outer plywood is equipped with the flange, the outer fringe of backup pad is equipped with the draw-in groove, fixes a position through groove and flange complex trip structure between the two, has realized the location of high accuracy when the welding. Be provided with the inner plating 16 parallel with outer plywood around skeleton 1 simultaneously, the inner plating is whole piece, including the linkage segment at the triangle section at both ends and middle part, each inner plating stands respectively on the skeleton with outer plywood parallel arrangement, is equipped with hinge 5 on the triangle section at one of them inner plating both ends, the other end and the upper cover 2 of hinge link to each other for form articulated between upper cover and the skeleton, open the upper cover when being convenient for and overhaul, and be equipped with radar support 21 in the middle part of upper cover 2 and be used for installing laser radar. And each side plate 3 is arranged to be an inverted trapezoidal plate matched with the inner plate, and the side plates are connected with the inner plate through bolts to seal the periphery of the framework.

As shown in fig. 1 and 2, the steering wheel assembly 4 is fastened to the wheel groove of the frame by bolts screwed into the mounting holes.

As shown in fig. 4, the steering wheel assembly 4 includes a driving wheel module 41, a steering module 42, and a connecting plate 43; the position of the connecting plate corresponding to the mounting hole is provided with a through hole, the steering wheel assembly is arranged in the wheel groove, the steering module is clamped in the framework, and the steering module is connected with the framework through a bolt which penetrates through the through hole and is screwed into the mounting hole. The driving wheel module is fixed below an output shaft of the steering module through six screws penetrating through the connecting plate 43, and the rotation of the output shaft of the steering module directly drives the driving wheel module to deflect left and right; steering wheel assembly passes through connecting plate

As shown in fig. 5 and 6, the driving wheel module 41 includes a wheel body 411, a driving motor 412, and a damping bracket 413. The wheel body 411 is an outer tire. The driving motor 412 is a hub motor matched with an outer-ring tire, the driving motor is embedded in a wheel body and is connected with the damping support 413 through a central shaft of the driving motor, threads are arranged outside the end parts of two ends of the central shaft of the driving motor, and a pair of planes are milled at the outer ends of the thread sections so as to clamp a wrench during connection.

The shock absorbing bracket 413 includes a lower bracket 4131, an upper bracket 4132 and a shock absorber 4133. The lower bracket 4131 is a U-shaped bracket, the root parts of two side plates of which are welded with a pin shaft 4134, the middle part of which is provided with a through hole, and the end part of which is provided with a threaded hole. The upper bracket is an n-shaped bracket, the top end of the upper bracket is provided with a circle of connecting holes, and the two sides of the bottom end of the upper bracket are connected with hinged seats 414. As shown in fig. 7, the hinge seat 4135 is a cylindrical seat body, the center of which is embedded with a wear-resistant sleeve 4136, the solid body is provided with a circle of connecting holes arranged in an annular array around the axial center, and the hinge seat is connected with the upper bracket through bolts penetrating through the connecting holes. The lower support is horizontally arranged, and two ends of the central shaft respectively penetrate through holes on two sides of the lower support and are matched with corresponding nuts to lock so as to complete the installation of the lower support; then the upper bracket is arranged in a downward inclined manner and sleeved outside the lower bracket, and is hinged through a rotating shaft bolt 4137 penetrating through a hinge seat 4135, a copper gasket is arranged between the upper bracket and the lower bracket, and the copper gasket is in contact limit with the hinge seat and the wear-resistant sleeve, so that a gap exists between the upper bracket and the lower bracket, and direct abrasion is avoided. The rotating shaft bolt 4137 comprises a cylindrical head, a polished rod section and a threaded section, the outer diameter of the cylindrical head is gradually decreased, the cylindrical head is a hexagon socket head, the rotating shaft bolt is sleeved in the wear-resistant sleeve through the polished rod section, and the threaded section is in threaded connection with the lower support. After the upper and lower brackets are mounted, the ends of the shock absorber 4133 are respectively sleeved outside the pin 4134 and positioned by a cotter pin 4138 passing through the radial hole. The steering module 42 is mounted on the top of the upper bracket, and is connected by bolts passing through the connection holes.

After the assembly of the driving wheel module 41 is completed, the shock absorber is triangular with the upper support and the lower support, the upper support is hinged with the lower support, a wear-resistant flexible rotating shaft structure is designed, the rotating shaft structure can rotate freely, the shock absorber is compressed when an obstacle is met, the lower support and the hub motor can rotate upwards around the position of the rotating shaft, the shock is reduced, and the large impact can be borne. For the pin joint, because install wear-resisting cover in the articulated seat, wear-resisting cover is interference fit with articulated seat. One end of the rotating shaft bolt is a threaded section, the middle section of the rotating shaft bolt is a precisely machined cylinder, one end of the rotating shaft bolt is a hexagonal socket head, and the threaded section and the middle section of the rotating shaft bolt are provided with a step. The cylindrical section of the rotating shaft bolt is arranged in the copper sleeve hole, and the thread section of the rotating shaft bolt penetrates through the copper gasket and is fixed on the lower support of the driving motor. The rotating shaft bolt and the copper sleeve are in clearance fit and can rotate freely, and the copper gasket is in contact spacing with the hinge base and the copper sleeve, so that a gap exists between the upper motor support and the lower motor support, and direct abrasion is avoided.

As shown in fig. 8 and 9, the steering module 42 includes a steering motor 421, a speed reduction mechanism 422, and a rotating shaft 423. Reduction mechanism 422 includes a final drive 4221 and a range drive 4222. The input end of the main reducer 4221 is connected with the steering motor, the output shaft is connected with the input gear of the auxiliary reducer, and the output end of the auxiliary reducer is connected with the rotating shaft. Two ends of an output shaft of the main speed reducer extend out of the main speed reducer, a high-magnetic steel sleeve 424 is arranged outside the top end of the output shaft, and an angle sensor 425 is arranged at a corresponding position below the steering motor so as to control the steering angle. The shell of the auxiliary speed reducer 4222 comprises an upper shell and a lower shell, a circle of groove is formed in the outer edge of the upper shell, matched protrusions are formed in the outer edge of the lower shell, and the upper shell and the lower shell are matched with the protrusions through the grooves to improve installation accuracy. The rotating shaft 423 is a stepped shaft, four convex clamping jaws 4231 are arranged at the top end of the rotating shaft, four clamping grooves are formed in an output gear of the auxiliary speed reducer, the rotating shaft is connected with the auxiliary speed reducer through the top end of the rotating shaft, the clamping jaws extend into the clamping grooves and fill eight damping rubber pads 426, impact in two directions of forward rotation and reverse rotation can be borne, and damage to the gear is avoided when impact occurs. The bottom of the rotating shaft is connected with the damping support through a bolt penetrating through the connecting hole.

The lower end of the output shaft of the main speed reducer is matched with an input gear of the auxiliary speed reducer by a D-shaped hole shaft. And a small deep groove ball bearing, a thrust ball bearing and a large deep groove ball bearing are sequentially arranged between the output end and the rotating shaft and between the output gear along the axial direction, and the three bearings are arranged in a cavity formed by an upper shell and a lower shell of the auxiliary speed reducer. The rotating shaft is a stepped shaft, the thrust ball bearings are arranged above the gear ring and mainly bear axial force, and the large deep groove ball bearings and the small deep groove ball bearings are arranged at two ends of the output shaft and bear radial force, so that the output shaft is always kept vertical.

Compared with the existing steering wheel, the steering wheel assembly in the embodiment integrates the driving motor and the wheel body into a whole by adopting the hub motor, has the advantages of simple and reliable structure, good protection, no gear transmission and no gear damage under the impact and emergency acceleration and deceleration environments. The steering module adopts a supporting structure, the steering motor and the angle sensor are integrally arranged, the size is small, and the control is simple. The support between the rotating shaft and the speed reducing mechanism adopts a combined bearing design, and has strong bearing capacity, small transverse size, small gap and small virtual position angle. The shock absorber is arranged, compared with other shock-absorbing steering wheels or robot chassis with shock absorption, the shock absorption system is additionally arranged outside the whole steering wheel, the shock absorption system has the advantages of small volume, simple structure and small unsprung mass, and the shock absorption rubber cushion is arranged between the rotating shaft and the output gear, so that the shock absorption system can play a role in buffering, is used for absorbing impact caused by impact of ground obstacles and enables the steering wheel to adapt to various road surfaces.

Compared with the existing chassis, the chassis adopts four-wheel independent suspension type, the driving wheels have good obstacle crossing capability, and the four steering wheel assemblies can respectively control steering and driving, so that the degree of freedom is high, and the control is flexible; the driving wheel adopts an integrated hub motor, is in gearless transmission, can adapt to rapid acceleration and deceleration in the walking process, and cannot damage gears; the framework is designed to be of a bearing type structure, the three-dimensional thin plates are welded in a splicing mode, the clamping tenon structure is located, and the framework has the advantages of being high in rigidity, strong in bearing capacity and light in weight.

Claims

1. A mobile robot chassis, characterized in that: the steering wheel assembly comprises a framework, an upper cover, side plates and a steering wheel assembly; the framework is a box body with a sunken middle part, the periphery of the framework is provided with a plurality of mutually independent wheel grooves, the upper edge of the framework is provided with support angles, and a slot is arranged between two adjacent support angles; the upper cover is arranged on the upper part of the closed framework on the supporting angle, the side plate is inserted into the slot to close the side surface of the framework, and each steering wheel assembly is respectively arranged in the corresponding wheel groove.

2. The mobile robot chassis of claim 1, wherein: the framework is a rectangular box body, the middle of the framework is a cross-shaped sinking cavity, four corners of the framework are steering engine mounting positions, through holes are formed in the top surface of each steering engine mounting position, and mounting holes are formed in the periphery of each through hole.

3. The mobile robot chassis of claim 2, wherein: the supporting angle comprises an outer plate and a supporting plate, the outer plate is a L-shaped plate attached to a framework corner, the supporting plate is a right-angle triangular plate, the top of the right angle is a circular arc attached to the outer plate, a clamping groove which penetrates through a bevel edge in parallel with the right-angle edge is formed in the supporting plate, and the supporting plate is connected to the top of the outer plate.

4. The mobile robot chassis of claim 3, wherein: the top of the outer plate is provided with a flange, the outer edge of the supporting plate is provided with a clamping groove, and the supporting plate is clamped with the outer plate and then welded.

5. The mobile robot chassis of claim 2, wherein: the inner layer plate is an integral piece and comprises triangular sections at two ends and a connecting section in the middle, each inner layer plate is respectively erected on the framework and arranged in parallel with the outer layer plate, the triangular sections at two ends of one inner layer plate are provided with hinges, and the other end of each hinge is connected with the upper cover; each side plate is arranged in the inner-layer plate.

6. The mobile robot chassis of claim 5, wherein: and the middle part of the upper cover is provided with a radar support.

7. The mobile robot chassis of claim 1, wherein: the steering wheel assembly comprises a driving wheel module and a steering module; the driving wheel module comprises a wheel body, a driving motor and a damping bracket, and the driving motor is connected with the driving wheel through the damping bracket; the steering module comprises a steering motor, a speed reducing mechanism and a rotating shaft, wherein an output shaft of the steering motor is connected with an input end of the speed reducing mechanism, an output end of the speed reducing mechanism is connected with the rotating shaft, and the other end of the rotating shaft is connected with the damping support; the driving motor drives the wheel body to rotate; the output power of the steering motor is transmitted to the rotating shaft to drive the damping support to steer after being decelerated by the decelerating mechanism.

8. The mobile robot chassis of claim 7, wherein: the shock absorption support comprises a lower support, an upper support, a shock absorber and a hinge seat; the lower bracket is a U-shaped bracket, and the middle parts of the two side plates are provided with through holes; the upper bracket is an n-shaped bracket which is obliquely arranged downwards, the top end of the upper bracket is provided with a circle of connecting holes, and the lower end of the upper bracket is hinged outside the lower bracket; the pair of shock absorbers are symmetrically arranged on the central plane of the wheel body in the thickness direction and are respectively arranged on the two sides of the upper bracket and the lower bracket; pin shafts are welded on two sides of the lower support, pin shafts are welded on two sides of the upper support, radial holes are formed outside the pin shafts, and two ends of the shock absorber are respectively sleeved outside the pin shafts and are positioned through split pins penetrating through the radial holes; a through hole is formed in the center of the hinge seat, a circle of connecting holes are formed in the periphery of the hinge seat, and a wear-resistant sleeve is embedded in the through hole; the hinged seat is connected with the upper bracket through a bolt penetrating through the connecting hole, and the upper bracket is sleeved outside the lower bracket and is connected with the lower bracket through a rotating shaft bolt penetrating through the wear-resistant sleeve; the rotating shaft bolt comprises a cylindrical head, a polished rod section and a threaded section, the outer diameter of the cylindrical head is gradually decreased, the cylindrical head is a hexagon socket head, the rotating shaft bolt is sleeved in the wear-resistant sleeve through the polished rod section, and the threaded section is in threaded connection with the lower support.

9. The mobile robot chassis of claim 8, wherein: the driving motor is a hub motor, threads are arranged at two ends of a central shaft of the hub motor, and planes are arranged at the outer ends of the thread sections; the driving motor is embedded in the wheel body, and the central shaft penetrates through the upper through hole of the lower bracket and is locked by matching with the nut; the speed reducing mechanism comprises a main speed reducer and an auxiliary speed reducer, the input end of the main speed reducer is connected with the steering motor, the output shaft of the main speed reducer is connected with the input gear of the auxiliary speed reducer, and the output end of the auxiliary speed reducer is connected with the rotating shaft; both ends of an output shaft of the main speed reducer extend out of the main speed reducer, and a strong magnetic steel sleeve is arranged outside the top end of the output shaft; an angle sensor is arranged at the position corresponding to the ferromagnetic steel sleeve under the steering motor; the shell of the auxiliary speed reducer comprises an upper shell and a lower shell, a circle of groove is formed in the outer edge of the upper shell, a matched protrusion is formed in the outer edge of the lower shell, and the upper shell and the lower shell are matched with the protrusion through the groove to improve installation accuracy.

10. The mobile robot chassis of claim 9, wherein: the pivot is the step shaft, and the top of pivot is equipped with the jack catch of evagination, establishes the draw-in groove in the output gear of vice reduction gear, and the pivot links to each other with its top and vice reduction gear, and the jack catch extends in the draw-in groove and packs the shock attenuation cushion, with its bottom with shock absorber support links to each other through the bolt that passes the connecting hole.